Crosslinking of Branched PIM-1 and PIM-Py Membranes for Recovery of Toluene from Dimethyl Sulfoxide by Pervaporation

Branched forms of the archetypal polymer of intrinsic microporosity PIM-1 and the pyridinecarbonitrile-containing PIM-Py may be crosslinked under ambient conditions by palladium(II) acetate. Branched PIM-1 can arise in polymerizations of 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane with tetrafluoroterephthalonitrile conducted at a high set temperature (160 °C) under conditions, such as high dilution, that lead to a lower-temperature profile over the course of the reaction. Membranes of PIM-1 and PIM-Py crosslinked with palladium acetate are sufficiently stable in organic solvents for use in the recovery of toluene from its mixture with dimethyl sulfoxide (DMSO) by pervaporation at 65 °C. With both PIM-1 and PIM-Py membranes, pervaporation gives high toluene/DMSO separation factors (around 10 with a 77 vol % toluene feed). Detailed analysis shows that the membranes themselves are slightly selective for DMSO and it is the high driving force for toluene evaporation that drives the separation.


S2. Purification of the Polymers.
Each recovered filtered polymer was re-dissolved in CHCl3 (concentration of 5 g in 120 mL) and re-precipitated by pouring slowly into excess methanol. The polymer was collected via filtration and refluxed in de-ionized water for 16 h. After refluxing in water, the mixture was filtered by vacuum filtration and then immersed in a minimal amount of 1,4-dioxane for 15 min (volume used was just enough to cover the mass of polymer in the beaker) to remove low molecular weight oligomers. The polymer was vacuum filtered before washing with excess of acetone to remove traces of 1,4-dioxane. The filtered polymer was then soaked in methanol for 12 h to remove all traces of dioxane and acetone. Finally, the polymer was filtered dry using a sintered funnel under vacuum, before drying in a vacuum oven at 120 °C for 72 h to remove all trace solvents.

S3. Polymer Characterization.
Size exclusion chromatography (SEC) analysis: Average molar masses of the polymers were measured by triple detector size exclusion chromatography (SEC). Analysis was performed in chloroform from 1 mg mL -1 polymer solutions (injection volume 100 µL) at a flow rate of 1 mL min −1 using a Viscotek VE2001 SEC solvent / sample module with two PL Mixed B columns maintained at 35 C and a Viscotek TDA 302 triple detector array (refractive index, light scattering, viscosity detectors). The data were analysed in OmniSec software.
Nuclear Magnetic Resonance (NMR) analysis: 1 H NMR spectra of the polymers were recorded using a Bruker Avance II 500 MHz instrument. 50 mg mL -1 polymer solutions in CDCl3 were prepared for the NMR analysis. Signal peaks for the solvent were used as references. An example of a 1 H NMR spectrum of a strongly branched PIM-1 polymer sample S7 (7) is presented later in Figure 3. The spectra obtained for the other PIM samples are provided in Figures S1−7. Lorentz peak fitting of the aromatic proton region ( = 6.0−7.2 ppm) of each proton NMR spectrum was used to determine the respective integral areas associated with resonances attributed to disubstituted PIM-1 residue and branch point stuctures (aromatic protons labelled a, b, c and d in Figure 1). Examples of the peak fittings obtained for the aromatic proton regions of 1 H NMR spectra of polymers, 5, 6, 7 and 8 are presented in Figures S8−11.
This allowed an estimation of the percentage of branch points present in each PIM polymer sample as a proportion of all residues present (calculations further outlined in Tables S3−S4 and results presented in Table 1).
Determination of network content. A polymer solution in chloroform (1 mg mL -1 ) was accurately prepared from 10-15 mg of a polymer sample. The entire solution was passed through a 0.45 m PTFE syringe filter and the exact weight of solution collected into a 30 mL sample bottle was recorded. The solvent in the bottle was allowed to slowly evaporate over several days.
Once the solvent had visually completely evaporated, the bottle was placed in an oven at 100 C to complete the drying process. The weight of polymer remaining in the bottle was measured and compared against the mass of filtered solvent (volume of chloroform) initially collected to determine the filtered polymer concentration. The network content by filtration was determined as the difference between the initial and filtered concentrations of the polymer as a percentage.

Fourier-Transform Infrared (FTIR) Spectroscopy: Analysis was performed on a Perkin Elmer
FTIR at a wavelength range of 600 -4000 cm -1 and a resolution of 4 cm -1 .

S4. Historical branched PIM-1 samples.
Historical polymerizations 1 and 2 involved minor variations on conditions previously utilized for PIM-1 synthesis and their 1 H NMR spectra indicate a significant amount of branched structures, 13.5 % and 6.5 %, respectively (Figures S1−2). For polymerization 1, an unspecified amount of additional solvent was added during the polymerization to lower the viscosity of the reaction mixture, which is also likely to have lowered the temperature profile during the polymerization. Polymerization 2 was carried out on a larger scale (0.5 mol rather than 0.05 mol), which is likely to have led to a slower rate of heating than when carried out at the smaller scale, so that the early stages of polymerization occurred at lower temperatures.